Warming Slowdown Was Real, Scientists Say

A global warming slowdown has come and gone, but an academic brouhaha continues to boil over the nitty gritty details of what once was a great scientific mystery.

On Wednesday, a group of prominent scientists published a commentary faulting colleagues who have published papers downplaying or dismissing the significance of a 13-year slowdown in warming rates at the planet's surface.

"We shouldn't sweep the early 2000s warming slowdown under the rug," said Penn State meteorology professor Michael Mann, one of 11 authors of the commentary published in Nature Climate Change.

Temperature measurements taken at the surface of the planet from 2001 to 2014 revealed a lull in the rate of global warming, sometimes called the "warming hiatus," before spiking upward again. Then 2014 was the hottest year on record until the record was easily beaten in 2015.

Until 2009, scientists had little explanation for the phenomenon. By 2014, though, it was known that the slowdown was caused primarily by a phase in a slow-moving Pacific Ocean cycle, with fierce trade winds driving more heat than normal into ocean depths.

Wednesday's commentary lauded the advances in climate science that helped solve the mystery of the slowdown, while rebuking other scientists whose research has concluded that the slowdown was insignificant or unimportant.

"Given the intense political and public scrutiny that global climate change now receives, it has been imperative for scientists to provide a timely explanation of the warming slowdown," wrote the 11 scientists, who are based in Canada, England, Australia and the U.S. "Despite recently voiced concerns, we believe this has largely been accomplished."

One of the studies singled out in the commentary was produced by National Oceanic and Atmospheric Administration scientists led by Thomas Karl, who directs the agency's National Climatic Data Center.

Karl's team believes some historical records of ocean temperatures are flawed, and they corrected them accordingly. The result of that analysis led them to conclude in a paper published last year in Science that warming during the early 2000s was "far more similar" to the longer-term trends "than previously estimated."

That surprise finding prompted Rep. Lamar Smith, a Republican from Texas who is chairman of the House Committee on Science, Space and Technology, to aggressively push for access to the government scientist's emails, part of an investigation that others have characterized as a witch hunt.

Smith has argued that the NOAA study was "expedited to fit" the Obama Administration's "aggressive" climate policies - a claim the agency strongly denies.

Karl on Wednesday stood by his work, saying "there is no disagreement" that temperatures and warming rates vary between decades. "We showed that one could not claim that the long-term warming trend was significantly different from the shorter period," he said.

Wednesday's commentary was a reminder that opposition to NOAA's findings is not just from politicians and fossil fuel groups, but from researchers who are convinced that the warming slowdown was real - and worthy of a public conversation.

The new commentary included new analysis of temperature data that showed what the authors described as a "mismatch" between early-century rates of warming and rates projected by model simulations.

"We're presenting results to support previous findings of reduced rates of surface warming," said John Fyfe, a Canadian government climate scientist who coordinated publication of the commentary. "That essentially refutes the Karl et al. paper."

Fyfe said he had "no doubt" that the commentary would be misused by climate science deniers, but that he had no hesitations about publishing it. "I don't think we should be in the business of pandering to the climate deniers."

Two other teams of scientists whose papers were critiqued in the commentary downplayed any differences in opinion, pointing to the consensus that global warming and natural variability both affected early-century surface temperatures.

"Their perspective is very much in line with our previously published work," said Noah Diffenbaugh, one of four Stanford researchers who wrote a paper published last year in Climatic Change provocatively titled "Debunking the climate hiatus." "Global warming has resulted in a long-term trend superimposed on natural climate variability."

Another paper criticized in the commentary was published last year by the Bulletin of the American Meteorological Society. In it, three scientists led by University of Bristol cognitive psychology professor Stephan Lewandowsky concluded that "there is no evidence that identifies the recent period" of warming as "unique or particularly unusual."

That paper argued against the use of the term "global warming hiatus," or "pause," which is sometimes used to describe the recent global warming slowdown.

You've heard a lot about how human-driven climate change will lead to hotter temperatures, cause sea levels to rise and make storms more intense. But it's projected to have plenty of other unpleasant and even disastrous effects as well. Here are 10 of them.
Scientists believe that rising temperatures will lead to increased evaporation of the Great Lakes' water, and precipitation won't make up the difference. That means we're likely to see declines in water levels over the next century, and one study predicts they may drop as much as 8 feet.

By altering the wild environment, climate change makes it easier for newly mutated microbes to jump between species, and it's likely that as a result, diseases will emerge and spread across the globe even more rapidly.

A recent Nature article reported that male Australian central bearded dragons have been growing female genitalia because of rising temperatures, a phenomenon that had not previously been observed in that species.

Rising sea levels are wiping out beaches all over the world already. Importing fresh sand and building them up again is only a temporary solution. To make matters worse, there's currently a sand shortage, due to demand from fracking, glass and cement making.

Warmer temperatures mean there will be more water vapor trapped in the atmosphere, leading to more lightning. A University of California-Berkeley study predicts that lightning strikes will increase by about 12 percent for every degree Celsius gained.

Wine grape harvests are being hurt. Regions that have historically supplied the world’s best wine will no longer be hospitable climates to grow wine grapes, according to research by the Environmental Defense Fund and others.

Coffee flavor depends upon really narrow conditions of temperature and moisture, and climate change is going to wreak havoc with that. Worse yet, as coffee growing regions become warmer, pests that couldn't survive in the past will ravage the crops. This is already being seen in Costa Rica, India and Ethiopia, which have experienced sharp declines in crop yields.